以賽局理論分析能量收集無線感測網路之隨機接取控制

Abstract

傳統無線感測網路以電池作為電源供應，然而一旦電池用盡，網路將陷入無法使用的困境，直至更新電池為止。但在某些無線感測網路應用當中，更換電池幾乎不可行，譬如建築監測感測系統。為了解決這問題，人們轉向使用可從環境汲取能源之能量收集無線感測網路。在這論文裡，我們建立了能量收集無線感測網路之隨機接取控制理論模型，探討眾多無線感測裝置爭取有限傳輸資源產生之問題。考慮無線感測裝置會自私地最大化自己的效用，所有裝置將會不顧系統整體效能選擇傳輸，使得系統陷入最糟情況。我們提出兩種激勵機制：收費機制和干擾機制，用以防止系統陷入最糟狀況。這兩種激勵機制可以誘使無線感測裝置選擇對系統而言最佳的策略，使系統達到社會最適(Social Optimal)、或是比例公平(Proportional Fair)的分配。在論文最後，我們深入探討無線感測裝置可選擇留存能源之延伸模型。我們發現，無線感測裝置會根據每段時間的能量收集機率，決定是否將能源留存至未來。在系統達成平衡之後，無線感測裝置會在能量收集機率較高的期間，選擇較高的傳輸機率。

Traditional wireless sensor networks (WSN) are powered by batteries. Once the batteries run out, the devices become useless until they are replenished. However, for some kinds of applications, such as building structure monitoring, it is nearly impossible to replenish the batteries of devices. To overcome this problem, people turn to the energy-harvesting(EH) WSNs which can harvest energy from the environment. In this work, we construct theoretic models where devices are competing for limited transmission resource. Since the devices are selfish, they all choose to transmit regardless of others’ strategy, which leads to the severe network congestion. We propose two incentive mechanisms, a pricing scheme and an intervention scheme, that prohibit the system outcome from the worst case. The incentive scheme can induce the desired optimal outcomes whichmaximize the social welfare or the proportional fairness. In the last part, we also build an extension model in which the energy can be stored for the future. We show that it is more likely that the device chooses to save some energy for the period when the energy harvesting probability is comparatively low. On the other hand, the devices will choose a higher transmission probability at the period when the energy harvesting probability is comparatively high.